8 Nature of the Genetic Material 



respective enzymes, but is molded by a template process involving 

 the surface of the molecule to be reduplicated. For the details of 

 this concept on a molecular basis see Pauling and Delbnick (1940) 

 and Friedrich-Freksa (1940); for its application to the genetic ma- 

 terial see also S. Emerson (1945). The idea requires the interimistic 

 production of a negative. Recently Watson and Crick ( lQ5Sa,b; 

 Crick, 1954) have proposed for the first time a molecular structure 

 which makes possible an understanding of how the template idea 

 works. We shall present the details later in our discussion. A variant of 

 the template ideas proposed by Haldane (1954) will be mentioned 

 below when discussing crossing over. 



Assuming the genetic material in the chromosome to consist of 

 a series of individual gene molecules, it would not be difficult to 

 visualize such a scheme of duplication if the old idea were true that 

 the chromosome disintegrates in the resting nucleus and is reas- 

 sembled at the time of division. The gene molecule floating in the 

 nuclear sap could proceed with re-creating its likeness as indicated. 

 The non-genic part of the chromosome could divide by real fission 

 and afterward adsorb the genes in their proper place, say by means 

 of specific haptenes comparable to those assumed to act in immunity 

 reactions. (If I am not mistaken, 1 first used such a scheme when I 

 tried a since disproved and discarded alternative explanation for 

 crossing over; Goldschmidt, 1917Z?. ) 



All the more recent developments of cytology point, however, 

 in the direction of a chromosome which remains more or less, if not 

 completely, intact in the interphase nucleus. Chromosomes have been 

 isolated by grinding up resting nuclei, even of cells like erythrocytes, 

 which do not divide further; as far as can be judged, the structure 

 and biochemistry of these chromosomes are normal (Claude and Pot- 

 ter, 1943; Mirsky and Ris, 1947a,b, 1951). (But doubts still exist in 

 regard to the chromosomal nature of the isolates; see Alfert's review, 

 1954.) Moreover, a number of cell types are known, like gland cells 

 of waterbugs (Geitler, 1940a, 1954) and tissue cells of Diptera, in 

 which the chromosomes in resting nuclei are visible, with their normal 

 structural details, because of polyteny and (or) giant size. Though 

 the visibility of the structural details seems to be an unusual feature 

 of these giant chromosomes, the presence of intact chromosomes may 

 be safely assumed for all interphase nuclei. It has been observed 

 many times that telophase chromosomes may double before restora- 

 tion of the daughter nucleus. Thus it may be considered certain that 

 whatever the genie material is, it divides or reduplicates with and 



